With recent evolution of portable information processing devices, various types of PC cards for memories, modems, facsimiles, LAN cards and the like have been commercialized. As higher performance and multi-function are increasingly demanded year by year, the size of an electronic component such as an LSI to be mounted on an inside printed board is increased.
Conventionally, there are various known structures for the PC cards, including a structure such that a printed board mounted with an electronic component such as a memory is incorporated in a frame and covered with a pair of metal covers from upper and lower sides (for example, JP7-160377A).
FIG. 3 is a partial sectional view of a common PC card of the prior art. In FIG. 3, reference numerals 1 and 100 denote an upper cover and a lower cover, respectively. The upper and lower covers are each formed of a thin metal plate, and include a major planar portion and a bend peripheral edge portion.
A reference numeral 3 denotes a printed board, which is composed of a rectangular plate of a synthetic resin. The printed board 3 is disposed between the upper cover 1 and the lower cover 100 in parallel relation, and electronic components 4, 5, 6 are mounted on front and back surfaces of the printed board 3.
A connector 7 is mounted on one edge of the printed board 3. Though not shown, the connector 7 is connected to a slot provided on a host side for signal transmission between the connector 7 and the host side.
A reference numeral 101 denotes a rigid frame molded from a resin. The printed board 3 is fixed in the frame 101 by an adhesive or screws. Further, the upper cover 1 and the lower cover 100 are respectively fixed to front and back sides of the frame 101 by a snap-in method or a fusion bonding method to protect the board 3.
However, the thickness of the PC card is specified to be 5 mm by the Standard. Therefore, if the electronic components 4, 5, 6 mounted on the printed board 3 have greater heights, the thickness of the printed board 3 or the thicknesses of the upper and lower covers 1, 100 should be correspondingly reduced.
Recently, multi-level printed boards have been used for higher density integration, so that the reduction of the thickness of the printed board is often impossible. If the thickness of the printed board is reduced, the printed board is liable to be deformed due to a temperature change or after mounting, thereby failing to ensure sufficient reliability.
Therefore, it is necessary to reduce the thicknesses of the planar portions of the upper and lower covers 1, 100. However, if the thicknesses of the upper and lower covers 1, 100 are reduced, the strength of the covers 1, 100 is correspondingly reduced. Therefore, the covers 1, 100 are liable to be deformed when the planar portions of the covers 1, 100 are pressed or the PC card is dropped. This reduces the reliability. In general, the planar portion of the cover 1 or 100 of the PC card has a shallow recess formed in a surface thereof for application of a label or the like. In this case, the thickness of the thinner planar portion of the cover 1, 100 is further reduced, so that the strength of the cover 1, 100 is further reduced.